The invention relates to a method of tempering or controlling the temperature of a printing press by a circulating temperature control medium, the temperature of which is regulated.
It is necessary to temper or control the temperature of a printing press in order to maintain the temperature-dependent viscosity of the printing ink processed in the printing press approximately constant. Otherwise, excessively large fluctuations in the viscosity of the printing ink would manifest themselves in the form of excessively large fluctuations in the optical color density measurable in the printed image.
For a very long time heretofore, efforts have been made for improving the temperature control of printing presses, as documented by the following, briefly described publications of the prior art.
British Patent 1 242 095 describes a method wherein a temperature measuring sensor is assigned to a feedline and forerunning flow line, respectively, for a temperature control medium.
German Utility Model DE-U 73 43 273 describes an inking unit wherein the temperature of a tempering or temperature control medium emerging from rollers is measured by measuring sensors which are assigned to respective discharge and return lines.
German Patent DE 42 11 379 C2, corresponding to U.S. Pat. No. 5,355,796, makes reference to temperature registration or determination by inserting thermocouples into a cooling system, and measuring the temperatures of the coolant respectively supplied and discharged.
German Published, Non-Prosecuted Patent Application DE 198 37 174 A1, corresponding to U.S. Pat. No. 6,164,207, describes the state of the art to which reference is made in the first paragraph of the introduction hereto. In that publication, a method of temperature control is described wherein a mixing container is provided to which machine oil flowing back from an ink duct roller and serving as a tempering or temperature control medium is supplied and into which machine oil having a temperature controlled by a cooling assembly is also introduced. A temperature measuring sensor and a temperature regulating device are also used in order to implement the method.
All of the prior art cited hereinbefore is unable to satisfactorily solve a problem in the tempering or temperature control of printing presses, which has existed for a relatively long time. The problem is that, on the one hand, a very long preheating and warm-up phase is required until the temperature of the press has been tempered or controlled to the required operating temperature thereof, if only the flow temperature of the tempering or temperature control medium supplied to one printing unit of the printing press serves as the measurement and control parameter in the tempering or temperature control. On the other hand, temperature fluctuations of up to 7 Kelvin of the tempering or temperature control medium are to be expected, which in turn cause intolerably large optical color density fluctuations in the printed image if, during the tempering or control of the temperature, only the return temperature of the tempering or temperature control medium discharged from the printing unit is used as a measurement and control parameter.
A similar problem exists in printing presses which are set up at locations with ambient temperatures above the operating temperature of the printing press and, therefore, require a respective precooling and cooling operating phase preceding production printing, the respective phase serving for adjusting the operating temperature. The precooling and cooling operating phase, during which the temperature control medium (in that case a cooling liquid) is circulated through the printing press while printing cannot yet be performed because the printing press temperature has not yet fallen sufficiently, lasts too long in the heretoforeknown methods.
It is accordingly an object of the invention to provide a method of tempering or controlling the temperature of a printing press, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and in which, during production printing, only tolerably small temperature fluctuations occur and the temperature control phase (cooling or warm-up operating phase) preceding production printing is not unnecessarily long.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of tempering a printing press by a circulating tempering medium, which comprises regulating a temperature of the tempering medium. The temperature at a first measurement location is measured for purposes of control during production printing by the printing press. The temperature at a second measurement location is measured during a tempering phase of the printing press preceding production printing.
In accordance with another mode, the method invention further includes providing a control device for regulating the temperature. The control device is changed over automatically from measuring at the second measurement location to measuring at the first measurement location the instant that the temperature deviates from a temperature limiting value prescribed for the control device.
In accordance with a further mode, the method invention further includes providing the first measurement location between a heater and an inlet for the tempering medium. The tempering medium is heated with the heater.
In accordance with an added mode, the method invention further includes providing the second measurement location between an outlet for the tempering medium and a heater. The tempering medium is heated with the heater.
In accordance with an additional mode, the method invention further includes providing the first measurement location between a cooler and an inlet for the tempering medium. The tempering medium is cooled by the cooler.
In accordance with yet another mode, the method invention further includes providing the second measurement location between an outlet for the tempering medium and the cooler. The tempering medium is cooled by the cooler.
In accordance with a concomitant mode, the method invention further includes providing a mixing tank for the tempering medium between the first measurement location and an inlet for the tempering medium. Temperature fluctuations of the tempering medium in the mixing tank for the tempering medium are damped.
The method according to the present invention is of the general type referred to in the introduction hereto but advantageously calls for measuring the temperature at a first measurement location for control during production printing. The temperature at a second measurement location is measured during a temperature control phase (cooling or warm-up phase) of the printing press, which precedes the production printing.
In the method according to the invention, the respective disadvantages of the flow measurement and flow temperature control heretofore known from the prior art, and of the return measurement or return temperature control likewise known heretofore from the prior art, are eliminated.
Through the use of the respective control and regulation strategy upon which the method invention is based, on the one hand, unnecessary prolongation of the tempering or temperature control phase of the printing press is avoided and, on the other hand, assurance is provided that the temperature of the tempering or temperature control medium only fluctuates extremely slightly during production printing.
It is inherent in the method according to the invention that the temperature of the tempering or temperature control medium can never be controlled or regulated from measured values measured simultaneously at the two measurement locations. Although it is possible for the temperatures to be measured simultaneously at both measurement locations, at the instant of the simultaneous measurement of the temperatures, it is always only one of the measured values obtained at the two measurement locations which is used for the control or regulation of the temperature of the tempering or temperature control medium. If, at a specific instant, the temperature of the tempering or temperature control medium is regulated based upon the measured value obtained at the first measurement location, then the measured value possibly obtained at this instant at the second measurement location is not used for regulating the temperature. If, at a different instant, the temperature of the tempering or temperature control medium is controlled based upon a measured value obtained at the second measurement location, then the measured value possibly obtained at the last-mentioned instant at the first measurement location is not used to control the temperature of the tempering or temperature control medium. Stated in other words, although the two measurement locations are used chronologically after one another, they are never used simultaneously for obtaining the measured values required for the control or regulation.
In a development which is advantageous with regard to relieving the load on the operating personnel for operational interventions, the temperature of the tempering or temperature control medium is regulated by a control device which is configured so that it switches or changes over automatically from using the second measurement location to using the first measurement location the instant the measured temperature either exceeds a temperature limiting value prescribed for the control device (if the temperature control phase is a warm-up phase) or falls below the temperature limiting value (if the temperature control phase is a cooling phase).
In a development which is advantageous with regard to controlling the flow temperature of the tempering or temperature control medium, in a manner unaffected by a printing unit of the printing press, during production printing, a heater serving to heat the tempering or temperature control medium (and/or a cooler serving to cool the tempering or temperature control medium) is provided between the first measurement location that is used and an inlet for the temperature control medium. The printing unit temperature, which fluctuates as a function of machine speeds of the printing unit, for example, can therefore no longer have a detrimental effect as a disruptive variable on the quality and accuracy of the temperature regulation of the tempering or temperature control medium in production printing. The aforementioned inlet for the tempering or temperature control medium is a printing unit inlet, preferably an inking unit inlet and, for example, a roller inlet.
In a development which is advantageous with regard to the use of a comparatively inexpensive control device for regulating the temperature of the tempering or temperature control medium, in order to damp temperature fluctuations of the tempering or temperature control medium supplied to the printing unit, use is made of a mixing tank or container for the tempering or temperature control medium, disposed between the first measurement location and the inlet. The temperature fluctuations, the magnitude of which depends upon the control accuracy of the regulating device, necessarily occur in each control device. The higher the requirements for the control accuracy and therefore the lower the temperature fluctuations, the more expensive is the requisite control device. As a result of the presence and the selected configuration of the mixing tank and the compensating tank connected directly upstream of the mixing tank, the temperature fluctuations necessarily caused by the existing control device are compensated for to the greatest possible extent, so that the requirements on the control accuracy of the existing control device can be kept low, and a comparatively inexpensive control device can be used as the latter. Although the existing control device needs to be only a particularly inexpensive two-point control device, for example, it is possible with such a device to achieve a high control accuracy, which is equivalent to the control accuracy of a much more expensive servocontroller, which is therefore not required.
In a development which is advantageous with regard to taking into account the rise in the printing unit temperature during the warm-up phase for controlling the temperature of the tempering or temperature control medium, the second measurement location that is used is disposed between an outlet for the temperature control medium and the heater that is used for heating the tempering or temperature control medium.
In a development which is advantageous with regard to taking into account the drop in the printing unit temperature during the cooling phase for controlling the temperature of the tempering or temperature control medium, the second measurement location that is used is disposed between an outlet for the temperature control medium and the cooler used for cooling the tempering or temperature control medium.
In both the developments just mentioned hereinbefore, the outlet for the temperature control medium is, respectively, a printing unit outlet, preferably an inking unit outlet and, for example, a roller outlet.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of tempering or controlling the temperature of a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.